Factors affecting the distribution of cetaceans in European Atlantic waters

Abstract

The waters of the European North Atlantic are subject to an increasing amount of anthropogenic pressure. Much of the environmental legislation designed to protect cetaceans requires detailed knowledge of the abundance and distribution of cetaceans within these waters. This data often comes from large-scale surveys. Data from two such series of surveys, spanning two time periods: the SCANS-II and CODA surveys in 2005/07 and the SCANS-III and ObSERVE surveys in 2016 were analysed using Generalised Additive Models to describe relationships between cetacean density and static and remotely accessed dynamic environmental features. Predictive models using spatial covariates as well as environmental predictors were created for the entire survey area using the most recently available data. This was done to conduct a “baseline” snapshot, representing the best possible picture of cetacean distribution for the summer of 2016. Subsequent chapters focus on specific ecoregions. These regions of relatively homogeneous habitat were selected with the aim of finding the best environmental predictors of genuine ecological relationships. In the North Sea ecoregion, models for harbour porpoise, minke whale, and white-beaked dolphin were also constructed using additional prey data available only for this region. This was found to be no better than modelling only environmental covariates. Depth was one of the most commonly retained covariates for all three species in this ecoregion. White-sided, bottlenose, common and striped dolphins and fin whale were investigated in the Celtic Seas, and Bay of Biscay and Iberian Peninsula ecoregions. Despite these two ecoregions being quite different, in most cases, model fits did not improve by including ecoregion as a factor covariate, suggesting that relationships between species and their environment were similar across both regions.